I'm studying for a test and in one of the solutions to a problem, Stirling's Approximation is used and allows the equation
(q+N−1)!q!⋅(N−1)!
to become
1q!⋅NN!⋅(q+N)!q+N
I don't understand how the last two terms came to be. Is it a factorial identity or is there underlying math that hasn't been shown in the solution.
